A GaN light-emitting diode (referred to as “LED” in the following) generally includes a semiconductor multilayer film that is formed by the crystal growth of a III-V group nitride semiconductor, expressed by a general formula of BzAlxGa1−x−y−zInyN1−v−wAsvPw (0≦x≦1, 0≦y≦1, 0≦z≦1, 0≦x+y+z≦1, 0≦v≦1, 0≦w≦1, 0≦v+w≦1), on a single crystal substrate such as a sapphire substrate. When a current flows through this semiconductor multilayer film, the GaN light-emitting diode can emit light in the wide range of ultraviolet to infrared regions (e.g., 200 nm to 1700 nm). In particular, a LED for emitting light in a wavelength region shorter than greenish blue is being developed at present.
Above all, a blue LED for emitting blue light is combined with a phosphor that emits yellow light or red light by excitation of the blue light, and can be used as a white LED for emitting white light (e.g., JP 11(1999)-40848 A). The white LED can have a longer life compared with incandescent lamps or halogen lamps and thus is expected to replace the existing lighting sources in the future.
As an example of a semiconductor light-emitting device including the white LED, FIG. 8 shows the cross section of a semiconductor light-emitting device disclosed in JP 11 (1999)-40848 A. As shown in FIG. 8, a semiconductor light-emitting device 100 includes a sapphire substrate 101, a semiconductor multilayer film 102 that is formed in contact with the sapphire substrate 101 and constitutes a blue LED, a Si substrate 103 that supports the semiconductor multilayer film 102, and a phosphor layer 104 that is formed on the Si substrate 103 to cover the sapphire substrate 101. An electric insulating film 105 and a conductor pattern 106 are formed in this order on the Si substrate 103. The conductor pattern 106 is connected electrically to the semiconductor multilayer film 102 via bumps 107 and an electrode 108.
The semiconductor light-emitting device 100 with the above configuration can be applied to a lighting unit generally in the following manner. As shown in FIG. 9, many semiconductor light-emitting devices 100 (although FIG. 9 illustrates only one of them) are mounted on a mounting board 201 to form a light-emitting module 200. This light-emitting module 200 is used as a light source of a lighting unit (not shown). In FIG. 9, the light-emitting module 200 includes the mounting board 201, a reflecting plate 203 that is fixed on the mounting board 201 via an adhesive layer 202 with a hollow 203a inside, the semiconductor light-emitting device 100 that is placed in the hollow 203a of the reflecting plate 203 and mounted on the mounting board 201, and a lens 204 that is formed on the mounting board 201 to cover the semiconductor light-emitting device 100 and the reflecting plate 203. The mounting board 201 includes a metal layer 205, and a first electric insulating layer 206, a wiring 207 and a second electric insulating layer 208 that are stacked in this order on the metal layer 205. The wiring 207 of the mounting board 201 and the conductor pattern 106 of the semiconductor light-emitting device 100 are connected electrically by a bonding wire 209.
However, the light-emitting module 200 is required to ensure a region for positioning the bonding wire 209. This may interfere with high integration of the semiconductor light-emitting device 100. Therefore, it would be difficult to increase the luminous flux of light produced by the light-emitting module 200.
As shown in FIG. 10, a light-emitting module 300 may be configured by using an AlN substrate 301 instead of the Si substrate 103 (see FIG. 8) and via conductors 302 instead of the bonding wire 209 (see FIG. 9) to connect the wiring 207 and the conductor pattern 106 electrically. In this case, however, there is a gap G between the AlN substrate 301 and the mounting board 201 (the first electric insulating layer 206), and thus heat generated from the semiconductor multilayer film 102 is not likely to be dissipated efficiently.